I put the MBC back on today.
It seems the culprit isn't the computer trying to normalize boost, it's the traction control system trying to limit wheel spin.
When I'm in autostick and know I will need to accelerate quickly I will tend to ride the gear I'm in a little higher in rpm's to be ready for when I need that extra go. Usually this will result in less tire spin than when the auto downshifts. I've noticed boost holds higher and longer in autostick because of this simple fact.
I tested WOT with traction control off and on and the difference is night and day. When my tires would brake loose with it on it would drop me to 4-5psi and then seem to hold around there. With the tc off I would get up to 11psi and hold in that neighbourhood.
This info has probably been posted before a number of times. It's just my slow way of putting 1 + 1 together.
The MBC is staying on now. Traction control is coming off when the need for speed is there.
Now to hit the local dyno.